There have been many attempted methods for providing for the slow release of fertilizer.
Lehr (U.S. Pat. No. 2,019,824) disclosed the use of "water resisting peat" produced by compressing a mixture of peat and fertilizer at 130-150 kg./sq. cm. without heat.
Treeland (U.S. Pat. No. 2,165,592) taught impregnating absorbent granular material, such as pulp or sawdust, with a saturated solution of ammonium sulfate, muriate of potash and water and mixing the impregnated granules with 90% powdered graphite and 10% carbon black to coat and to close the pores of the granules which are mixed with super Phosphate and black loam soil.
Genz (U.S. Pat. No. 1,944,788) proposed the in situ formation of plant nutrients in industrial waste products, such as tobacco stems by treating stems impregnated with the acid or basic constituent of the nutrient with an acid or alkali to produce crystalline salts in the matrix.
Rose (U.S. Pat. No. 371,630) taught the use of vegetable material being used to adsorb "tank water" (water from the rendering of lard, tallow and other fats), then dried and used as fertilizer.
Bierlich (U S. Pat. No. 2,498,480) employs various cellulosic refuse as a carrier for chemical fertilizer. The cellulosic material is purified or depitched, then chemical fertilizer is added under pressure along with bentonite to retain it in the cellulosic material.
Hoblit (U.S. Pat. No. 3,252,785) discloses spraying a mixture of ammonia and/or urea nitrogen, phosphoric acid, potassium as K.sub.2 SO or KCl and a dye onto a particulate carrier, e.g., cobs, nutshells and sawdust, and other dry ingredients such as ureaform and potash, whereby some of the nutrient solution is absorbed into the granules and the balance of the solution coats the granules and binds the other dry ingredients to the granules.
Sherwin et al (U.S. Pat. No. 3,940,257) mixed one part of seaweed with 10 parts of tree bark and pulverized the mixture so that the juice of the seaweed is absorbed by the bark.
A slow-release fertilizer according to Attoe (U.S. Pat. No. 3,059,379) encloses soluble fertilizer in water-impervious bags provided with a plurality of perforations.
Trocino's slow release fertilizer (U.S. Pat. No. 3,929,446) is derived from Douglas fir bark, previously dewaxed and freed of cork with an organic solvent, after which bark is mixed with liquid fertilizer and pelletized.
The use of expanded vermiculite, nutrient material and a binder to prepare a slow-release fertilizer is disclosed by Barron in U.S. Pat. No. 3,369,884.
Barton (U.S. Pat. No. 3,953,191) employs cotton gin waste as a carrier for fertilizer. The waste material is heated in a superheated chamber at 215 degrees F., and 30 p.s.i., with a fertilizer and pelletized.
A slow-release fertilizer according to Taylor (U.S. Pat. No. 3,672,945) consists of a solid core of inert material, such as solid fertilizer or nutshells, and a water-soluble inert adhesive. This material is coated with a powder of finely ground calcite, dolmite, sand, clay or pumice, to which agricultural chemicals or nutrients are applied.
Heming et al (U.S. Pat. No. 3,645,714) describe preparing a slow release fertilizer of tree bark, which is hammer milled to pass 90% through a 10 mesh screen, mixed with water and a commercial fertilizer, and pelleted.
Baskin (U.S. Pat. No. 3,558,299) prevents caking of particulate urea by coating with 3-5% of a conditioner selected from the group consisting of finely divided clay, talc, mica, vermiculite, powdered nutshells and pulverized corn cobs blended with urease.
Slow-release fertilizers are also prepared by coating granules of fertilizer with an insoluble substance. Examples are Smith (U.S. Patent No. 3,150,955), who used area-formaldehyde; Zaayenga (U.S. Pat. No. 3,192,031), who used wax, and Hanson (U.S. Pat. No. 3,264,089), who used organic resins. Pole (U.S. Pat. No. 2,806,773) taught the use of silicates and water insoluble organic resins to coat minor element particles and adhere them to inert carriers.
Sticks, stakes and cartridges have been used to release fertilizer slowly into the soil. Antrium (U.S. Pat. 2,032,608) produced a fertilizer stake by compressing a mixture of cellular fibrous material and a binder with a large amount of water and a fertilizer. Laffler et al (U.S. Pat. No. 2,931,140) disclosed a cartridge with small holes in the nose cone to slowly release the fertilizer. Gessler (U.S. Pat. No. 3,057,713) described a fertilizer stick made form a mixture of super phosphate fertilizer, asbestos, phosphoric acid and water. Prack (U.S. Pat. No. 3,060,012) disclosed a cartridge of sawdust, corn cobs or other organic material, nutrients and waterproofing chemicals. The cartridge is made with a series of concentric rings designed to release nutrients slowly. Schenk (U.S. Patent No. 3,502,458) teaches that a rigid slow-release fertilizer stake that can be driven into the ground is made by mixing a dry fibrous organic material, e.g., corn cobs, peat moss or cloth linters, a dry fertilizer and at least 3% binder and heating the mixture up to 380 degrees F. at a pressure of 100-8000 p.s.i. to form a rigid mass.
Wahlberg (U.S. Pat. No. 4,246,018), who produces a fertilizer from tree bark, adds yeast to waste molasses to ferment the molasses and lower the pH thereof before combining and treating the molasses and crushed tree bark at elevated temperature and pressure.
Sproull et al (U.S. Pat. No. 3,218,149) feeds a pre-heated nutrient solution to a pre-heated base material, e.g., bark or sawdust to a mixing reactor where the nutrient materials are chemically bound to the base by chemical reactions. The combined fertilizer, mulch and soil conditioner releases nutrients only as the base material decays.
Ford (U.S. Pat. No. 4,145,202) incorporates grass seed and nutrients in comminuted peanut hulls, which have been freeze-dried in order to increase voids in the hulls and, consequently, receptivity to the seeds and nutrients.
In the above-mentioned application, Serial No. 850,522, peanut hulls were proposed as a carrier for liquid plant nutrients impregnated thereon to provide a slow-release fertilizer. However, the release of the nutrients is not as uniform and long-lasting as desired. Until the present invention, in fact, there were no important uses for peanut hulls. They could not be used as mulch or as organic material since they did not degrade and, furthermore, they have been found to promote the growth of Fusarium, to the detriment of desirable plant growth, and Aspergillus, which produces Aflatoxins.
Each of the prior-art slow-release fertilizers is intended to allow nutrients to remain in the soil near plants treated therewith for extended periods of time so that the nutrients are released gradually and become available to the plants. However, the presently available products have one or more deficiencies, including:
(1) variable rate of nutrient release,
(2) undesirably high rate of nutrient release, which is wasteful and possibly damaging to plants,
(3) undesirably high ratios of carrier to nutrient,
(4) deficiency of one or more essential nutrients,
(5) poor storage life,
(6) carrier is not bio-degradable and not a source of nutrients.